(M0930-06-35) Dust Emissions of Surrogate Substances Resulting from Diffusive and Convective Transport for Containment Investigations with a Newly Developed Two-Chamber Setup

Purpose: In a previous study, the dust emissions of the industry-accepted safe surrogate substances acetamino­phen (ACAM) and naproxen (NAP) were monitored using a newly developed two-chamber setup. The purpose of this study was to compare the dustiness of both surrogate substances resulting from diffusive and convective transport.

Methods: In Figure 1, a simplified illustration of the newly developed two-chamber setup is shown. The setup consists of an emission chamber and a detection chamber both connected by an orifice with a diameter of 25.4 mm. The separation of the chambers was performed by a controllable flap. The dimensions of the emission chamber are 300 mm × 300 mm × 300 mm resulting in a volume of 27 l. The detection chamber shows the same dimensions, but its pyramidal construction leads to a smaller volume of approximately 15 l. The double-acting ball valve above the emission chamber was applied to atomize 100 mg of the surrogate substances by compressed air for a time period of 5 s. The adjustable flow conditions of the two-chamber setup depend on the differential pressure between the detection chamber and the emission chamber. To obtain a convective or diffusive transport of the airborne particles, the controllable flap was opened for 60 s. The convective transport of the airborne particles from the detection chamber to the emission chamber was generated by an adjustable airflow via the second double-acting ball valve which is located above the detection chamber. The pressure difference was adjusted to 0 Pa for the diffusive transport and to 1 or 2 Pa for the investigation of the convective transport to obtain a directed flow from the detection chamber to the emission chamber. After the 60 s, the controllable flap was closed and the dust in the detection chamber was evacuated through an IOM sam­pler with an air sampling pump at a flow rate of 5 L/min for 9 min. The quantitative analysis of ACAM (true density: 1.2886 g/cm³ ± 0.0024 g/cm³ (mean ± SD, n = 3); particle-size distribution (PSD): x₁₀: 1.67 µm ± 0.08 µm; x₅₀: 8.36 µm ± 0.30 µm; x₉₀: 24.33 µm ± 0.90 µm) and NAP (true density: 1.2497 g/cm³ ± 0.0054 g/cm³; PSD: x₁₀: 3.31 µm ± 0.04 µm; x₅₀: 11.49 µm ± 0.23 µm; x₉₀: 26.80 µm ± 0.99 µm) was carried out by high performance liquid chromatography (HPLC). In Figure 2, a simplified piping and instrumentation diagram for the control of the valves and pneumatic devices is shown. The valves were actuated by a programmable logic controller.

Results: In Figure 3, the results of the dustiness investigations of ACAM and NAP resulting from diffusive and convective transport are summarized. The diffusive transport of ACAM and NAP is characterized by a higher dust emission than that of the convective transport. The dust emissions caused by the diffusive transport of ACAM were 2.26 or 2.95 times higher than those caused by the convective transport with 1 or 2 Pa, respectively. In comparison, the dust emissions of NAP caused by diffusive transport were 3.28 or 3.90 times higher than that of the convective transport with 1 or 2 Pa, respectively. In general, the dust emission of ACAM is higher than that of NAP. The diffusive dust emission of ACAM was 1.19 times higher than that of NAP. As compared to ACAM, the convective dust emission of NAP decreased by 1.74 or 1.58 times at differential pressures of 1 or 2 Pa, respectively.

Conclusion: In the present study, it was shown that a newly developed two-chamber setup for containment investi­gations enables the comparison of the dust emission of the surrogate substances ACAM and NAP. In addition, these data demonstrate that the dust emission at each flow condition of ACAM was higher than that of NAP. The generation of convective flow conditions from the detection chamber to the emission chamber decreases the transport of dust compared to the diffusive transport conditions. It is assumed that the reasons for the differences in dust emission between ACAM and NAP might be electrostatic charges.


Figure 1: Simplified illustration of the two-chamber setup for containment investigations.


Figure 2: Simplified piping and instrumentation diagram for the valve control of the two-chamber setup.


Figure 3: Comparison of the mean dust emissions of ACAM and NAP ± SD (n = 3) resulting from diffusive and convective transport.